U.S. patent application number 13/832559 was filed with the patent office on 2014-02-27 for optical semiconductor device.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Keisuke Matsumoto, Yoshifumi Sasahata, Masakazu Takabayashi, Tohru Takiguchi. Invention is credited to Keisuke Matsumoto, Yoshifumi Sasahata, Masakazu Takabayashi, Tohru Takiguchi.
Application Number | 20140056556 13/832559 |
Document ID | / |
Family ID | 50148053 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140056556 |
Kind Code |
A1 |
Sasahata; Yoshifumi ; et
al. |
February 27, 2014 |
OPTICAL SEMICONDUCTOR DEVICE
Abstract
An optical semiconductor device includes: semiconductor lasers
separated into two groups; an optical coupler combining light
output from the semiconductor lasers; an optical amplifier
amplifying light output from the optical coupler; and waveguides
respectively connecting the semiconductor lasers to the optical
coupler. Each of the waveguides includes a respective bent
waveguide. The bent waveguides have the same radius of
curvature.
Inventors: |
Sasahata; Yoshifumi; (Tokyo,
JP) ; Takiguchi; Tohru; (Tokyo, JP) ;
Matsumoto; Keisuke; (Tokyo, JP) ; Takabayashi;
Masakazu; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sasahata; Yoshifumi
Takiguchi; Tohru
Matsumoto; Keisuke
Takabayashi; Masakazu |
Tokyo
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
50148053 |
Appl. No.: |
13/832559 |
Filed: |
March 15, 2013 |
Current U.S.
Class: |
385/31 |
Current CPC
Class: |
H01S 5/0265 20130101;
G02B 6/122 20130101; H01S 5/4031 20130101; G02B 6/2813 20130101;
G02B 2006/1215 20130101; H01S 5/34306 20130101; H01S 5/026
20130101; G02B 6/0001 20130101; H01S 5/227 20130101; B82Y 20/00
20130101 |
Class at
Publication: |
385/31 |
International
Class: |
F21V 8/00 20060101
F21V008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2012 |
JP |
2012-182906 |
Claims
1. An optical semiconductor device comprising: a plurality of
semiconductor lasers separated into two groups; an optical coupler
combining light output from the semiconductor lasers; an optical
amplifier amplifying light output from the optical coupler; and a
plurality of waveguides respectively connecting the semiconductor
lasers to the optical coupler, wherein the plurality of waveguides
includes respective bent waveguides, and the respective bent
waveguides all have the same radius of curvature.
2. The optical semiconductor device according to claim 1, wherein
each bent waveguide includes two circular arcs having same radius
of curvature and different curvature centers.
3. The optical semiconductor device according to claim 1, wherein
the plurality of waveguides includes respective straight
waveguides, and lengths of the respective waveguides of the
plurality of waveguides are equal to each other.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical semiconductor
device including the plurality of semiconductor lasers connected to
the optical coupler by a plurality of bent waveguides, and in
particular to an optical semiconductor device which can reduce
variation in line width of output lights when the plurality of
semiconductor lasers are respectively driven.
[0003] 2. Background Art
[0004] In an optical semiconductor device in which output lights
from a plurality of semiconductor lasers are combined by a
multi-mode interference (MMI) coupler and amplified by a
semiconductor optical amplifier (SOA), the plurality of
semiconductor lasers are connected to the optical coupler by a
plurality of bent waveguides (see, for example, Japanese Patent
Laid-Open Nos. 2009-109704 and 2004-319893 and Japanese Patent No.
4444368).
SUMMARY OF THE INVENTION
[0005] Variation in loss at the conventional semiconductor optical
amplifier is large because the plurality of bent waveguides have
different radii of curvature, so that the quantities of return
light to the plurality of semiconductor lasers vary and the output
lights from the plurality of semiconductor laser vary in line
width.
[0006] In view of the above-described problems, an object of the
present invention is to provide an optical semiconductor device
which can reduce variation in line width of output lights when the
plurality of semiconductor lasers are respectively driven.
[0007] According to the present invention, an optical semiconductor
device includes: semiconductor lasers separated into two groups; an
optical coupler combining output lights from the semiconductor
lasers; an optical amplifier amplifying output light from the
optical coupler; and a plurality of waveguides respectively
connecting the semiconductor lasers to the optical coupler. The
plurality of waveguides respectively includes bent waveguides. The
bent waveguides have same radius of curvature.
[0008] The present invention makes it possible to reduce variation
in line width of output lights when the plurality of semiconductor
lasers are respectively driven.
[0009] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a top view of an optical semiconductor device
according to a first embodiment of the present invention.
[0011] FIG. 2 is an enlarged top view of a portion of the device
shown in FIG. 1.
[0012] FIG. 3 is a top view showing the bent waveguide according to
the first embodiment of the present invention.
[0013] FIG. 4 is a sectional view of the semiconductor laser taken
along line I-II in FIG. 1.
[0014] FIG. 5 is a sectional view of the MMI coupler taken along
line III-IV in FIG. 1.
[0015] FIG. 6 is a sectional view of the SOA 3 taken along line
V-VI in FIG. 1.
[0016] FIGS. 7 to 10 are sectional views showing the process of
manufacturing the optical semiconductor device according to the
first embodiment.
[0017] FIG. 11 is a top view of an optical semiconductor device
according to the comparative example.
[0018] FIG. 12 is an enlarged top view of a portion of the device
shown in FIG. 11.
[0019] FIG. 13 is a top view of an optical semiconductor device
according to a second embodiment of the present invention.
[0020] FIG. 14 is an enlarged top view of a portion of the device
shown in FIG. 13.
[0021] FIG. 15 is a top view of an optical semiconductor device
according to a third embodiment of the present invention.
[0022] FIG. 16 is an enlarged top view of a portion of the device
shown in FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] An optical semiconductor device according to the embodiments
of the present invention will be described with reference to the
drawings. The same components will be denoted by the same symbols,
and the repeated description thereof may be omitted.
First Embodiment
[0024] FIG. 1 is a top view of an optical semiconductor device
according to a first embodiment of the present invention. FIG. 2 is
an enlarged top view of a portion of the device shown in FIG. 1. A
plurality of semiconductor lasers 1a to 1l are disposed by being
separated into two groups. An MMI coupler 2 combines output lights
from the plurality of semiconductor lasers 1a to 1l. A SOA 3
amplifies output light from the MMI coupler 2. A plurality of bent
waveguides 4a to 4l respectively connect the plurality of
semiconductor lasers 1a to 1l to the MMI coupler 2. The plurality
of bent waveguides 4a to 4l have the same radius of curvature of
1000 .mu.m.
[0025] FIG. 3 is a top view showing the bent waveguide according to
the first embodiment of the present invention. Each of the
plurality of bent waveguides 4a to 4l is formed of two circular
arcs having the same radius of curvature of 1000 .mu.m and
different curvature centers.
[0026] FIG. 4 is a sectional view of the semiconductor laser taken
along line I-II in FIG. 1. An n-type InP clad layer 6, an InGaAsP
quantum well active layer 7, a p-type InP clad layer 8, a
diffraction grating 9 and a p-type InP layer 10 are successively
stacked on an n-type InP substrate 5. These layers form a ridge,
two sides of which are buried by a p-type InP burying layer 11, an
n-type InP blocking layer 12 and a p-type InP current blocking
layer 13.
[0027] A p-type InP layer 14 and a p-type InGaAs contact layer 15
are successively stacked on the p-type InP layer 10 and the p-type
InP current blocking layer 13. A mesa 16 is provided outside the
ridge. The surface is covered with an insulating film 17 and an
opening 18 is formed in the insulating film 17 at a position for
electrode contact. A p-type electrode 19 is provided on the p-type
InGaAs contact layer 15. An n-type electrode 20 is provided on a
lower surface of the n-type InP substrate 5. The diffraction
gratings 9 of the plurality of semiconductor lasers 1a to 1l differ
in pitch from each other because of use as a wavelength variable
laser.
[0028] FIG. 5 is a sectional view of the MMI coupler taken along
line III-IV in FIG. 1. An n-type InP clad layer 6, an InGaAsP
waveguide layer 21 and an undoped InP layer 22 are successively
stacked on the n-type InP substrate 5. These layers form a ridge.
In other respects, the construction of the MMI coupler is the same
as that of the semiconductor lasers. Also, each of the bent
waveguides 4a to 4l is identical in structure to the MMI coupler 2
except that the ridge width is smaller. FIG. 6 is a sectional view
of the SOA 3 taken along line V-VI in FIG. 1. The structure of the
SOA 3 is the same as that of the semiconductor lasers except that
the diffraction grating 9 is not provided.
[0029] The process of manufacturing the optical semiconductor
device according to the present invention will be described. FIGS.
7 to 10 are sectional views showing the process of manufacturing
the optical semiconductor device according to the first embodiment.
FIG. 8 corresponds to portions of the semiconductor lasers 1a to 1l
and the bent waveguides 4a to 4l coupled to each other. FIG. 9
corresponds to portions of the MMI coupler 2 and the SOA 3 coupled
to each other. FIG. 10 corresponds to a portion of the MMI coupler
2.
[0030] First, as shown in FIG. 7, the n-type InP clad layer 6, the
InGaAsP quantum well active layer 7, the p-type InP clad layer 8
and a p-type InGaAsP diffraction grating layer 23 are grown in a
crystal growth manner on the n-type InP substrate 5 by a metal
organic chemical vapor deposition (MOCVD) method.
[0031] Next, as shown in FIG. 8, a diffraction grating pattern is
formed of an insulating film at the positions at which the
semiconductor lasers are to be formed, and the p-type InGaAs
diffraction grating layer 23 is etched by using the insulating film
as a mask to form the diffraction gratings 9. By this etching,
portions of the p-type InGaAsP diffraction grating layer 23 other
than those at the semiconductor laser formation positions are
removed. After removal of the insulating film, the p-type InP layer
10 is grown.
[0032] Next, as shown in FIG. 9, the surface is covered with an
insulating film at the positions at which the semiconductor lasers
1a to 1l and the SOA 3 are to be formed. Etching to the InGaAsP
quantum well active layer 7 is then performed by dry etching or the
like using the insulating film as a mask. Further, the n-type InP
clad layer 6 is slightly removed. The InGaAsP waveguide layer 21
and the undoped InP layer 22 are then grown selectively. The
insulating film is thereafter removed.
[0033] Next, as shown in FIG. 10, an insulating film 24 is
patterned, and etching to an intermediate portion of the n-type InP
substrate 5 is performed by using this insulating film 24 as a mask
to form a ridge. The p-type InP burying layer 11, the n-type InP
blocking layer 12 and the p-type InP current blocking layer 13 are
then grown. After removal of the insulating film 24, the p-type InP
layer 14 and the p-type InGaAs contact layer 15 are grown.
[0034] Next, an insulating film that covers surfaces portions other
than those on the semiconductor lasers 1a to 1l and the SOA 3 is
formed and the p-type InGaAs contact layer 15 is etched by using
this insulating film as a mask. After removal of the insulating
film, an insulating film is newly formed and patterned and the
semiconductor lasers 1a to 1l and the SOA 3 are etched by using
this insulating film as a mask to form the mesa 16. The insulating
film is thereafter removed. Next, the insulating film 17 is formed,
the opening 18 in the insulating film is formed at the portions for
electrode contacts, and the p-type electrode 19 and the n-type
electrode 20 are formed.
[0035] The operation of the optical semiconductor device according
to the present embodiment will now be described. One semiconductor
laser capable of obtaining the necessary oscillation wavelength is
selected from the plurality of semiconductor lasers 1a to 1l and
driven. Output light from this semiconductor laser is guided
through the bent waveguide connected to this semiconductor laser
and the MMI coupler 2 to enter the SOA 3. The SOA 3 amplifies this
output light. However, the laser light is reflected at reflection
points, e.g., the end surface, a butt joint and the MMI coupler.
Return light from each reflection point passes through the bent
waveguide and enters the semiconductor laser.
[0036] The effect of the present embodiment will be described in
comparison with a comparative example. FIG. 11 is a top view of an
optical semiconductor device according to the comparative example.
FIG. 12 is an enlarged top view of a portion of the device shown in
FIG. 11. In the comparative example, because a plurality of bent
waveguides 4a to 4l have different radii of curvature, variation in
loss is large. Therefore, the quantities of return light to the
plurality of semiconductor lasers 1a to 1l vary and the output
lights from the plurality of semiconductor laser 1a to 1l vary in
line width.
[0037] In contrast, in the present embodiment, variation in loss is
reduced since the radii of curvature of the plurality of bent
waveguides 4a to 4l are equal to each other. Therefore, the
differences between the quantities of return light to the plurality
of semiconductor lasers 1a to 1l can be reduced to reduce variation
in line width of output lights when the plurality of semiconductor
lasers 1a and 1l are respectively driven.
[0038] Here, the loss is maximized in the outermost bent waveguides
4a and 4l, and is minimized in the innermost bent waveguides 4f and
4g. Variation in loss was calculated by setting .DELTA.x of the
outermost bent waveguides 4a and 4l to 760 .mu.m, setting .DELTA.y
of these waveguides to 150 .mu.m and setting the radii of curvature
of these waveguides to 1000 .mu.m. In the calculation results,
while variation in loss in the comparative example was 3.3 dB,
variation in loss in the present embodiment was 2.1 dB. Thus,
variation in loss can be reduced by 1.2 dB in comparison with the
comparative example.
Second Embodiment
[0039] FIG. 13 is a top view of an optical semiconductor device
according to a second embodiment of the present invention. FIG. 14
is an enlarged top view of a portion of the device shown in FIG.
13. Straight waveguides 25a to 25j are inserted between the
plurality of bent waveguides 4b to 4k having the same radius of
curvature and the plurality of semiconductor lasers 1b to 1k so
that the lengths of the waveguides between the plurality of
semiconductor lasers 1a to 1l and the MMI coupler 2 are equal to
each other.
[0040] In this way, variation in loss can be further reduced in
comparison with the first embodiment. Therefore, the differences
between the quantities of return light to the plurality of
semiconductor lasers 1a to 1l can be further reduced to further
reduce variation in line width of output lights when the plurality
of semiconductor lasers 1a and 1l are respectively driven.
[0041] Variation in loss was calculated by setting .DELTA.x of the
outermost bent waveguides 4a and 4l in which the loss is maximized
to 760 .mu.m, setting .DELTA.y of these waveguides to 150 .mu.m and
setting the radii of curvature of these waveguides to 1000 .mu.m.
As a result of the calculation, variation in loss in the present
embodiment can be further reduced by 0.35 dB in comparison with the
first embodiment.
Third Embodiment
[0042] FIG. 15 is a top view of an optical semiconductor device
according to a third embodiment of the present invention. FIG. 16
is an enlarged top view of a portion of the device shown in FIG.
15. Straight waveguides 25a to 25j are inserted between the
plurality of bent waveguides 4b to 4k having the same radius of
curvature and the MMI coupler 2 so that the lengths of the
waveguides between the plurality of semiconductor lasers 1a to 1l
and the MMI coupler 2 are equal to each other.
[0043] In this way, variation in loss can be further reduced in
comparison with the first embodiment. Therefore, the differences
between the quantities of return light to the plurality of
semiconductor lasers 1a to 1l can be further reduced to further
reduce variation in line width of output lights when the plurality
of semiconductor lasers 1a and 1l are respectively driven.
[0044] Variation in loss was calculated by setting .DELTA.x of the
outermost bent waveguides 4a and 4l in which the loss is maximized
to 760 .mu.m, setting .DELTA.y of these waveguides to 150 .mu.m and
setting the radii of curvature of these waveguides to 1000 .mu.m.
As a result of the calculation, variation in loss in the present
embodiment can be further reduced by 0.35 dB in comparison with the
first embodiment.
[0045] In the first to third embodiments, the quantum well active
layer is InGaAsP. However, the present invention is not limited to
this. The quantum well active layer may alternatively be InAlGaAs,
for example. The radius of curvature is not limited to 1000 .mu.m.
The radius of curvature may alternatively be 500 .mu.m or 2000
.mu.m, for example. The number of semiconductor lasers is not
limited to 12. The number of semiconductor lasers may be 12 or
more, for example. The structure of the bent waveguides 4a to 4l is
not limited to the burying structure. The structure of the bent
waveguides 4a to 4l may alternatively be a mesa structure.
[0046] Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
[0047] The entire disclosure of Japanese Patent Application No.
2012-182906, filed on Aug. 22, 2012, including specification,
claims, drawings, and summary, on which the Convention priority of
the present application is based, is incorporated herein by
reference in its entirety.
* * * * *